Ethernet is a family of computer network standards that are widely used in wired local area networks (LANs). These standards have been codified by the IEEE 802.3 working group and define a wide range of link-level protocol features and medium access control (MAC) functions. The term “link” is used in the context of the present description and in the claims in its conventional sense to mean a direct physical connection between a pair of network nodes.
For full-duplex links, Annex 31B of the IEEE 802.3 specification defines an optional flow control operation using “PAUSE” frames. When the receiver on a given link transmits a PAUSE frame to the transmitter, it causes the transmitter to temporarily stop all transmission on the link (except certain control frames) for a period of time that is specified in the PAUSE frame. This pause mechanism enables the receiver to recover from states of congestion.
Recently, a number of new IEEE standards for data center bridging (DCB) have been proposed, offering enhanced Ethernet flow control capabilities. For example, the IEEE 802.1Qbb project authorization request (PAR) provides priority-based flow control (PFC) as an enhancement to the pause mechanism described above. PFC creates eight separate virtual links on a given physical link and allows the receiver to pause and restart the virtual links independently. PFC thus allows the operator to implement differentiated quality of service (QoS) policies for the eight virtual links.